Biomarker & Molecular Testing in Lung Cancer: An Overview

Why molecular testing matters here

Few solid tumors have been reshaped by molecular profiling as profoundly as non-small cell lung cancer (NSCLC). What was once treated as a small number of histologic categories is now understood as a collection of molecularly defined diseases, many driven by a single actionable alteration — an "oncogene-addicted" biology in which the tumor depends on one dominant signaling event [1]. The practical consequence is that a pathologic diagnosis alone is no longer sufficient to orient therapy. A growing panel of predictive biomarkers determines eligibility for specific drug classes, and the number of these classes has expanded rapidly, including seven new molecularly targeted approvals in 2025 alone [2].

This page is a hub. Each biomarker named below links to a dedicated detail article; here the goal is to orient readers to what is tested, why, and how results steer treatment at the level of drug class — never individualized treatment advice.

What gets tested, grouped by purpose

Diagnostic / lineage context

Histologic classification and immunohistochemistry (IHC) remain the entry point [3]. Molecular testing then layers predictive information on top. In lung cancer the great majority of validated biomarkers are predictive (they gate a therapy class) rather than purely prognostic, which is why testing is tightly coupled to treatment selection.

Predictive / therapy-gating biomarkers

Kinase-activating mutations and fusions — the classic targetable drivers:

• EGFR mutation — the archetype. Subtype matters greatly: exon 19 deletions and L858R are classic sensitizing variants; exon 20 insertions behave distinctly; T790M signals acquired resistance; and atypical variants (S768I, L861Q, G719X) form a separate group [4,5].
• ALK rearrangement — a gene fusion detectable by IHC screen with molecular confirmation [4].
• ROS1 rearrangement — fusion present versus absent, IHC-screened and molecularly confirmed [4].
• RET fusion — detected by NGS or FISH [4].
• MET exon 14 skipping — best captured by RNA-based NGS [1].
• NTRK fusion — a tumor-agnostic target; pan-TRK IHC screens, NGS confirms [4].
• BRAF V600E mutation — the V600E variant specifically (non-V600 is distinct) [4].
• KRAS G12C mutation — the specific G12C variant is required; other KRAS variants are not addressed by current G12C agents [6].
• ERBB2 / HER2 mutation — an activating mutation, distinct from amplification or overexpression [4].

Protein-expression biomarkers — increasingly relevant for antibody-drug conjugates (ADCs) and immunotherapy:

• PD-L1 expression — scored as a Tumor Proportion Score (TPS: <1%, 1–49%, ≥50%), assay- and antibody-specific [7].
• MET protein overexpression (c-MET IHC) — distinct from METex14 skipping and MET amplification; a newer IHC arm in the MET algorithm [2].
• TROP-2 — expression-based selection, with methods still maturing [2].

How results steer treatment (result → drug class)

Each biomarker result maps to eligibility for a therapy class, not to a personalized prescription.

• EGFR sensitizing (exon 19 del / L858R) → EGFR tyrosine kinase inhibitors (TKIs), including later-generation agents; indications extend into adjuvant and stage III (post-chemoradiation) settings. Exon 20 insertions → distinct targeted agents. T790M → signals resistance guiding subsequent TKI choice [4,5].
• ALK fusion present → ALK TKIs, with an adjuvant indication in early-stage disease [4,8].
• ROS1 fusion present → ROS1 TKIs [9].
• RET fusion present → selective RET inhibitors [10].
• METex14 skipping present → MET TKIs [1].
• NTRK fusion present → TRK inhibitors (tumor-agnostic) [11].
• BRAF V600E → combined BRAF + MEK inhibition, available first-line [12].
• KRAS G12C → KRAS G12C inhibitors (sotorasib, adagrasib), positioned after prior systemic therapy [6,13].
• HER2-mutant → HER2-directed ADC (trastuzumab deruxtecan) [14].
• c-MET high by IHC → MET-directed ADC (telisotuzumab vedotin, accelerated approval 2025) in previously treated disease [2,15].
• TROP-2 expressing → TROP-2-directed ADC (datopotamab deruxtecan), approved in 2025 for metastatic EGFR-mutated NSCLC after prior EGFR-targeted therapy [2,16].
• PD-L1 TPS → gates and stratifies immune checkpoint inhibitor therapy; monotherapy is generally favored at high TPS (≥50%), and PD-L1 is relevant across histologies including squamous [7,17].

The evidence supporting these links derives from the pivotal trials and companion diagnostic approvals cited throughout; the level of maturity varies by target, and several ADC-selection strategies remain works in progress.

Specimen and testing realities

Tissue versus liquid. Most biomarkers can be assessed on FFPE tumor tissue, plasma circulating tumor DNA (ctDNA), or both. ctDNA ("liquid biopsy") is valuable when tissue is scant, when a rapid answer is needed, or for tracking resistance such as EGFR T790M [4]. However, ctDNA has lower sensitivity, and a negative plasma result does not exclude an alteration — tissue confirmation remains important. Fusion detection (ALK, ROS1, RET, NTRK, METex14 skipping) is often better served by RNA-based NGS, which captures splicing and rearrangement events that DNA-only assays may miss [1].

Assay choice by biomarker. IHC serves as a rapid, sensitive screen for several targets (ALK, ROS1, pan-TRK, BRAF VE1) with molecular confirmation, and as the primary readout for PD-L1, c-MET, and TROP-2. FISH remains an option for rearrangements and amplifications. Broad NGS panels efficiently interrogate mutations and fusions simultaneously — increasingly the pragmatic backbone given the number of targets [1,4].

Reflex testing. Because the biomarker list is long and turnaround affects care, laboratories increasingly perform reflex molecular testing at diagnosis on eligible specimens, so results are available when treatment decisions are made rather than requiring sequential add-on orders. Comprehensive up-front profiling reduces the risk of tissue exhaustion from repeated single-gene tests.

What's emerging (fast-moving areas — flagged)

Several areas are evolving quickly and readers should expect the landscape to shift:

• ADCs and protein-expression selection. The 2025 approvals of telisotuzumab vedotin (c-MET IHC) and datopotamab deruxtecan (TROP-2) mark a shift toward protein-expression biomarkers as therapy gates [2,15,16]. Selection biology for TROP-2 in particular is still maturing, and optimal quantitative thresholds are not settled [16].
• The MET diagnostic algorithm now spans three distinct concepts — METex14 skipping, MET amplification, and c-MET overexpression — each with different assays and implications; conflating them is a common pitfall [2].
• ctDNA-guided monitoring for response and resistance is an active research area, with clinical roles still being defined.
• Expanding resistance profiling. As targeted therapy moves earlier (adjuvant, stage III), the biomarkers used to detect acquired resistance and to sequence subsequent therapy classes are under continued investigation [4].

The overall direction is clear: comprehensive, up-front molecular profiling — combining IHC, NGS, and selective liquid biopsy — is now foundational to lung cancer care, and the catalog of actionable results continues to grow.

References

1. Research progress in oncogene-addicted NSCLC. Cancer Biol Med. 2025.
2. Seven new FDA approvals in 2025 across molecular targets in NSCLC (review). 2025.
3. WHO Classification of Tumours Editorial Board. Thoracic Tumours, 5th ed. IARC, Lyon; 2021.
4. Lung Cancer: Targeted Therapy in 2025 (review). Curr Oncol. 2025.
5. Fehrenbacher L, et al. EGFR TKI as first-line treatment for advanced EGFR mutation-positive NSCLC. 2017. PMCID: PMC5650459.
6. KRAS G12C inhibitor approvals (sotorasib 2021, adagrasib 2022). FDA.
7. Khunger M, et al. PD-L1 expression as a predictive biomarker: analysis of FDA approvals of immune checkpoint inhibitors. J Immunother Cancer. 2019. PMC6815032.
8. FDA. Alectinib as adjuvant treatment for ALK-positive NSCLC. 2023.
9. FDA Approval Summary: Repotrectinib for ROS1-positive NSCLC. 2024. PMID:38875108.
10. Markham A, et al. FDA Approval Summary: Selpercatinib for RET-altered lung and thyroid cancers. 2021. PMID:33239432.
11. Drilon A, et al. Larotrectinib and Entrectinib: TRK Inhibitors for NTRK Gene Fusion cancers. J Hematol Oncol. 2021. PMC7863124.
12. Planchard D, Popat S, Kerr K, et al. Dabrafenib plus trametinib in BRAF V600E-mutant metastatic NSCLC. Lancet Oncol. 2017.
13. FDA Approval Summary: Sotorasib for KRAS G12C-mutated metastatic NSCLC. 2022. PMC9012672.
14. Li BT, et al. Trastuzumab Deruxtecan in HER2-Mutant Metastatic NSCLC: DESTINY-Lung02. J Clin Oncol. 2023. PMID:37694347.
15. FDA. Accelerated approval of telisotuzumab vedotin-tllv for NSCLC with high c-MET overexpression. 2025.
16. TROPION-Lung01: Datopotamab Deruxtecan versus Docetaxel in previously treated advanced NSCLC. J Clin Oncol. 2024. PMID:39250535.
17. Update 2025: Management of NSCLC (review). 2025.